Bump importlib-metadata from 0.18 to 0.19

Bumps [importlib-metadata](http://importlib-metadata.readthedocs.io/) from 0.18 to 0.19.

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Author: dependabot-preview[bot]

test-requirements.txt

@@ -19,7 +19,7 @@ entrypoints==0.3          # via flake8
 flake8==3.7.8
 idna==2.8
 immutables==0.9
-importlib-metadata==0.18  # via pluggy, pytest
+importlib-metadata==0.19  # via pluggy, pytest
 ipython-genutils==0.2.0   # via traitlets
 ipython==7.6.1
 isort==4.3.21             # via pylint